For the purpose of further improvement of the mechanical properties such as strength, rigidity, and heat resistance which a polyamide resin originally has, it has been a common practice to incorporate, into a polyamide resin, various fillers including, for example, inorganic fibers such as glass fibers or carbon fibers, inorganic compounds such as calcium carbonate, mica or talc, or layered compounds such as montmorillonite and swelling fluorine mica. Although being effective for improving the strength or rigidity of the resulting molded products, these methods are accompanied with the drawback that toughness which is another characteristic of the polyamide resin is markedly impaired owing to a low affinity of the polyamide with a filler. On the other hand, Japanese Patent Laid-Open No. 217454/1991 discloses a polyamide resin composition comprising 100 parts by weight of a polyamide and 5 to 300 parts by weight of apatite aiming at obtaining a material having a touch feeling close to ivory. However, this composition is improved in strength and rigidity of the resulting molded product like the compositions having other filler added thereto, but a markedly low affinity at the interface between the polyamide and apatite causes a drastic decrease in toughness, that is, decrease in tensile elongation, which makes it difficult to use it as an industrial material.
Thus, the present inventors have proposed a polyamide resin comprising a polyamide and an apatite having a high interfacial adhesiveness to the polyamide as disclosed in Japanese Patent Laid-Open No. 199771/1999. Especially, a polyamide resin obtained by a process of mixing a polyamide raw material and an apatite raw material and carrying out the polymerization of the polyamide and the synthesis of the apatite exhibits remarkably high improving effect of interfacial adhesiveness, which enables the realization of the physical properties which conventional polyamide resins cannot be achieved. That is, they have found a polyamide resin having improved rigidity and strength without impairing toughness.
However, as a result of the studies by the inventors, the rigidity and strength of the above polyamide resin can be improved without impairing toughness, but the moldability at, for example, injection molding, film forming, and blow molding for manufacturing various parts is not satisfactory in the application to various parts such as automobile parts, electronic/electrical parts, and industrial machine parts. Moreover, durability such as weathering resistance and heat resistant aging of the resulting molded products is also still unsatisfactory in the case that they are used as exterior parts of automobiles which are exposed to flaming sun in summer or as under-hood parts neighboring an automobile engine of a high temperature.
By the way, it is well known in the art to improve moldability by incorporating a lubricant such as a higher fatty acid metal salt into a polyamide resin. Moreover, it is also well known to improve weathering resistance or heat resistant aging property by adding a mixture of a metal halide and a copper compound.
However, upon the studies by the inventors, it was found that the simple application of these conventional technologies to the above polyamide resin comprising an polyamide and an apatite type compound does not result in a satisfactory improvement in the objective properties.
An object of the present invention is to provide a polyamide resin composition and a molded product thereof which can overcome the above-described problems, of the polyamide resin comprising an polyamide and an apatite type compound which have so far remained unsolved, in other words, a composition which is excellent in various moldability at, for example, injection molding, film forming, extrusion, and blow molding, the resulting molded product being excellent in strength, rigidity, heat resistance, and toughness, as well as durability such as surface appearance, weathering resistance, and heat-resistant aging property.